An engine is usually provided with a water pump for forcibly circulating coolant through the engine. The water pump rotates at a speed proportional to a rotation speed of the engine.
In general, a heating function of a vehicle has a close dependence on the coolant temperature. When a heater switch is turned on, hot air is immediately supplied to an interior room in the case that the coolant temperature is high, but in the case that the coolant temperature is low, only cold air can be supplied to the interior room until the coolant temperature is appropriately raised. When the engine is driven at a low speed, the coolant temperature does not rise quickly, so response to the heater switch becomes very slow.
In order to more quickly heat the interior room, some vehicles are provided with an additional heating apparatus in an air circulation duct system, for heating air passing therethrough. Such an additional heating apparatus causes volumetric efficiency of the interior room to be deteriorated and also causes cost of production to be raised. In addition, additional energy consumed for driving such an addition heating apparatus acts as an additional load on the engine, so fuel efficiency of the engine is deteriorated.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art that is already known in this country to a person of ordinary skill in the art.